Op-Amp Noise Calculator

Op-amp circuits generate noise from multiple sources — the amplifier itself, resistor currents, and thermal effects — and the Op-Amp Noise Calculator breaks down exactly how much each one contributes to your output. Enter your op-amp's voltage noise (En) and current noise (In+) from the datasheet, along with your source resistance, feedback resistor (R1), input resistor (R2), bandwidth, temperature, and circuit gain. You'll get the total output noise plus individual contributions from voltage noise, current noise, and thermal noise — alongside the signal-to-noise ratio in dB.

nV/√Hz

Op-amp voltage noise density from datasheet

pA/√Hz

Op-amp current noise density from datasheet

Ω

Source impedance driving the op-amp

Ω

Feedback resistor value

Ω

Input resistor for non-inverting input

Hz

Circuit bandwidth for noise integration

°C

Operating temperature for thermal noise calculation

V/V

Overall circuit gain

Results

Total Output Noise

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Voltage Noise Contribution

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Current Noise Contribution

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Thermal Noise Contribution

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Signal-to-Noise Ratio

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Frequently Asked Questions

What is op-amp noise and why does it matter?

Op-amp noise consists of voltage noise and current noise that limit the minimum signal that can be accurately amplified. It's critical in low-signal applications like sensor interfaces and audio circuits.

How do I find voltage and current noise specifications?

Check the op-amp datasheet for 'Input Voltage Noise' (nV/√Hz) and 'Input Current Noise' (pA/√Hz). These are typically specified at room temperature and 1 kHz frequency.

What is thermal noise and how is it calculated?

Thermal noise is generated by resistors due to random electron motion. It equals √(4kTR) where k is Boltzmann's constant, T is temperature in Kelvin, and R is resistance.

How does source resistance affect total noise?

Higher source resistance increases both thermal noise and current noise contribution. The current noise multiplied by source resistance becomes a voltage noise source.

Why is bandwidth important in noise calculations?

Noise power is proportional to bandwidth. Total RMS noise is the noise density multiplied by the square root of bandwidth. Limiting bandwidth reduces total noise.

What's the difference between spot noise and integrated noise?

Spot noise is noise density at a specific frequency (nV/√Hz), while integrated noise is total RMS noise over a bandwidth range. This calculator provides integrated noise.

How can I minimize op-amp circuit noise?

Use low-noise op-amps, minimize source resistance, choose appropriate feedback resistor values, limit bandwidth, and consider the trade-offs between voltage and current noise.

Does temperature significantly affect noise performance?

Yes, thermal noise increases with temperature. At higher temperatures, both resistor thermal noise and some op-amp noise sources increase, degrading overall performance.